An aerogel is a porous material having one of the highest levels of porosity, of up to 99%, of any known solid. The silica aerogel, which is a common type of inorganic aerogel, may be obtained by forming a gel, by subjecting a silica precursor solution to a sol-gel condensation reaction, and then drying the gel under supercritical conditions or ambient-pressure conditions, to yield an aerogel having a porous structure full of air. Due to its highly porous structure, as noted above, an aerogel is prone to shattering, and thus in practical applications, the aerogel may be placed in a particular container (e.g. a skylight panel) or combined with a fabric matrix into a composite body (e.g. a mat), to be used in a commercially available product having a physically stable structure.
With the conventional technology for manufacturing a mat containing silica aerogel, the mat may easily undergo an increase in density when it is manufactured under ambient drying conditions. This is because, as the ambient drying method may involve replacing the pore water with a volatile organic solvent and removing the solvent at or above the vaporizing temperature, there may be drying shrinkage caused by solid/liquid interfacial forces from the water or organic solvent remaining within the silica network. Since the attractive characteristics of the aerogel, such as super insulation, light weight, soundproofing, and low permittivity, are manifested by its unique porous structure of having 90-99% of the internal space empty, the shrinkage described above can make it more difficult for the aerogel to provide these characteristics. The counter-measures against this shrinkage problem according to the related art are to perform the drying under supercritical conditions, under which there is no solid/liquid interfacial forces, or to strengthen the silica network and improve the adhesion with fiberweb by adding an expensive alkoxide and aging in the alkoxide during an intermediate process.
Also, if inexpensive water glass is used in place of the expensive alkoxide material in an effort to reduce manufacturing costs, the process may become more complicated and additional costs may be incurred, because of the additional sol-preparation process through ion exchange columns and the numerous rounds of wet-gel cleansing in order to remove impurities present in water glass.
Also, since an unmodified, hydrophilic gel is impregnated into fibers and subjected to a hydrophobic modification reaction, the fibers can be damaged, and the adhesion between the fibers and the aerogel may be weakened, resulting in the aerogel flaking off as powder from the composite body after drying.
Korean Registered Patent No. 10-0385829, which relates to manufacturing a composite body using silica aerogel, teaches a method that uses water glass or an alkoxide as raw material and applies hydrolysis to produce a sol. First, when using an alkoxide as the raw material, a fiber web is immersed in a sol, and the consecutive processes of aging, replacing pore water, and surface-modification are applied, followed by ambient pressure drying. When water glass is used as a starting material, the manufacture does not include drying under normal pressure and instead uses a supercritical apparatus for the drying. Consequently, the costs of the raw materials were reduced, but an expensive supercritical apparatus has to be used, and it is impossible to perform the manufacture continuously.
Also, in the disclosure of Korean Registered Patent No. 10-0710887, the materials of water glass and an alkoxide are mixed together in a certain ratio, a fiber web is immersed in the mixed solution, and the processes of aging, replacing pore water, and surface-modification are applied, after which drying is performed under normal pressure. Here, while increasing the relative percentage of the alkoxide led to lower density (0.11-0.14 g/mL) and greater pore volume (2-4 g/cc) and pore size (14-26 nm), the properties of the fiber composite manufactured using only water glass showed a high density (0.2 g/mL), small pore volume (1.5 g/cc) and small pore size (10 nm).
As set forth above, using a conventional manufacturing method may be the complicated, discontinuous, and expensive process for obtaining the silica aerogel fiber composite that provides the mechanical strength. As such, there is active research to produce a silica aerogel composite in an ambient environment in pursuit of a simple and lowcost manufacturing process.